This invention relates to a plastic foam material. More specifically, this invention relates to a plastic foam material composed of a blended resin composition containing thermoplastic resins and a silane-modified resin (hereinafter referred to as "plastic foam material") and products derived therefrom. The present invention is also directed to a method of making the plastic foam material.
The present invention is also directed to a plastic foam material which has resin walls which include lattice-shaped or honeycomb-shaped cross-sections with foam inside. The present invention also relates to a method for making the same.
The plastic foam material of the present invention and products derived therefrom exhibit improved softness and superior heat-insulating properties. They are thus capable of being used as heat-insulating materials. Because of their softness, superior heat-insulating properties and lightness, products derived from the plastic foam material of the present invention, can be used extensively in many applications in different fields.
Products composed of the plastic foam material of the present invention are well suited for use as building materials. Such building materials include ceilings and installment panels. Due to their superior heat- insulating properties, the plastic foam material will find widespread use as aircraft, train and automobile components such as panels and seating. Various plastic foam material composed of resin compositions are commercially available but almost all of them are inferior in either heat resistance or foam generation. Most prior resin compositions which form prior art plastic foam materials exhibit excessive gel fractions and inner stresses imparting inferior qualities to conventional plastic foam materials and their derived products.
Notwithstanding increased heat resistance properties of conventional plastic foam materials, prior art plastic foam materials are well known for generating less foam and yielding foam materials that have inadequate compression strength. Accordingly, conventional plastic foam materials and their derived products are not suited for use inside buildings, as building materials or as materials for use inside automobiles, trains, and aircraft.
Many attempts have been proposed to overcome the aforementioned drawbacks. Unfortunately, to date the proposed improvements have been insufficient.
One such attempt at improving the overall quality of prior art plastic foam materials, disclosed in Japanese Laid Open Patent Publication S 58-134131, includes using a cross-linked polypropylene based resin composition as the starting material. The cross-linked polypropylene based resin composition further includes a silane-modified polypropylene based resin, together with a silanol condensation catalyst and a foaming agent.
However, the proposed resin composition is plagued by numerous drawbacks. Chief among them is the even cross-linking among the various constituents when a cross-linking agent is added to the starting material. Since the starting material includes a polypropylene based resin composition which is thermally grafted by an ethylene type unsaturated silane compound, the entire plastic foam material is evenly cross-linked upon addition of a cross-linking agent. This, in turn, increases the inner stresses within the plastic foam material, particularly upon heating.
Moreover, the amount of the silane-modified resin added to the proposed mixture is excessive compared to the other resin. The excessive silane-modified resin results in even cross-linking among the various constituents, resulting in an increase in the gel fraction of the resulting plastic foam material. The increased gel fraction of the plastic foam material, in turn, causes a subsequent decrease in the moldability of the plastic foam material. The decrease in the moldability properties of the plastic foam material, in turn, results in articles which are considerably weak and easily breakable. The derived products are unable to maintain and retain their shapes, due, in part, to the compromised moldability of the plastic foam material.
In an attempt to improve the compression strength of conventional plastic foam material and products derived therefrom, Japanese Laid-Open Publication No. S52-104574 discloses a method for making a foam compound that uses two extruders, where one extruder extrudes a plastic containing a foaming agent to form a core, while the other extruder extrudes plastic to cover the thus formed core. This is injected into a metal mold and foamed.
However, because this method involves the injection into a metal mold of a plastic containing a foaming agent and a separate covering plastic, it is difficult to provide a uniform feed of the plastic containing the foaming agent.
Thus, it is impossible to form a plastic column that penetrates both the front and back of the resulting plastic foam material. It is even less possible to form a plastic column uniformly in the plastic foam material. Thus, the compression strength of the resulting plastic foam material is inadequate.
On the other hand, honeycomb structures are porous and have high compression strength. A honeycomb structure involves a honeycomb form sandwiched between surface materials.
Notwithstanding the presence of the honeycomb structure which increases compression strength, conventional plastic foam materials according to this publication exhibit increased heat conductivity. This is because of the convection which results from an increase in internal space. The honeycomb structure thus imparts inadequate insulating properties to the resulting plastic foam material.
Japanese Laid Open Publication No. 4-151238 also attempts to improve the compression strength of conventional plastic foam materials by using a resin foam material connected to a fiber-reinforced resin layer by a plurality of columns. The space between the layers is filled with foam, except for the space occupied by the resin columns.
However, the reinforcing effect of this resin foam material is ineffective because resin columns are embedded in foam and thus are not continuous. Additionally, to effectively increase the compression strength of the resin foam material, it is deemed necessary to embed a large number of columns, making the resin foam material substantially heavy.
In an attempt to overcome the aforementioned deficiency, Japanese Laid-Open Patent Publication S61-59339 discloses a plastic foam material composed of a resin composition containing a copolymer consisting of ethylene and an unsaturated silane, a silanol condensation catalyst and a foaming agent.
According to this publication, a copolymer containing at least ethylene and unsaturated silane compound, among others, can be used instead of the copolymer containing an ethylene like olefin resin and the unsaturated silane copolymer.
However, the proposed plastic foam material composed of the aforementioned resin composition exhibits a high gel fraction and increased thermal deformation. The gel fraction has been reported to be substantially high. The increase in gel fraction and thermal deformation makes such a plastic foam material unsuitable for use in molding the proposed plastic foam material into large objects requiring increased stability.
Japanese Laid Open Patent Publication S56-109229 proposes the use of a plastic foam material composed of a silyl-modified ethylene based polymer together with an ethylene based polymer, and a foaming agent.
The proposed resin composition contains a substantial amount of a silane-modified ethylene based polymer per 100 parts by weight of the ethylene based polymer.
However, articles made of the disclosed plastic foam material exhibit increased inner stress. The inner stress, in turn, causes extensive thermal deformation.
None of the prior art references manage to overcome the problem of the high gel fractions and inner stresses.